This invention relates to chucks such as are used for holding drill bits in drills. The invention is also applicable to other chuck-like tool holders such as collets. For convenience herein and in the appended claims all such tool holders will be referred to generically as chucks.
It is known to provide chucks with nose structures which form a seal around a tool held in the chuck to help keep dust and debris from the workpiece out of the chuck. The nose structure may also help to keep the tool centered while the chuck is being tightened on the tool, and it may prevent the tool from dropping out of the chuck when the chuck is loosened. Chucks with nose structures having some or all of these properties are shown in Whitehead U.S. Pat. No. 4,575,108, Theissig et al. U.S. Pat. No. 4,664,394, Rohm U.S. Pat. No. 4,695,066, Huff et al. U.S. Pat. No. 5,135,241, and commonly assigned, co-pending application Ser. No. 08/045,557, now U.S. Pat. No. 5,299,814.
Perhaps the most frequently seen of the above-described structures is a relatively thin rubber membrane over the distal end of the chuck. The membrane has a hole through it coaxial with the central longitudinal axis of the chuck. A tool to be held by the chuck is pushed through this hole. The membrane surrounds the tool and keeps it centered as the chuck is tightened on the tool. During use of the tool the membrane keeps dust and debris from entering the chuck mechanism. And when the tool is no longer needed in the chuck, the membrane keeps the tool from falling out of the loosened chuck until the user deliberately pulls the tool out of the membrane.
A possible shortcoming of the known nose structures of the foregoing type is that the rubber membrane may wear out relatively quickly and thereby cease to perform its intended functions. For example, some tools become quite hot during use, and this heat may cause rapid deterioration of the membrane. The membrane is also at or near the front of the chuck where it may be exposed to contact with workpieces or workpiece debris that can damage it. Thus, in general, the remainder of a chuck typically has a much longer lifespan than the rubber membrane that may be provided on the chuck for such purposes as have been described. Yet in most cases, once the membrane has worn out, there is no convenient way to repair or replace it.
In view of the foregoing, it is an object of this invention to provide improved nose structures for chucks.
It is another object of this invention to provide nosepieces for chucks which are readily removable and replaceable when the rubber membrane of the nosepiece wears out.